The present invention relates to an air drier arrangement, comprising an air compressor, an air drier, an air conduit from the compressor to the air drier and an air conduit from the air drier to an air tank or an air consumer.
It is generally known that it is important to keep the inlet temperature to an air drier within a certain span, for example +4xe2x88x92+65xc2x0 C., but actually as low as possible. In many applications, when a so called governor mode for the control of the arrangement is used, this leads to problems with freezing in the air conduit between the compressor and the air drier.
Namely, in the governor mode the air flow stops, when the compressor is unloaded, leading under certain circumstances to a temperature drop below the freezing point. One advantage with this mode, however, is its energy saving ability.
When on the other hand a so called on-line unloader mode for the control of the arrangement is used, non-pressurized air blows through said conduit from the compressor and out to the atmosphere via the unloader valve of the air drier, when the arrangement is unloaded.
From an energy conserving viewpoint this system has disadvantages, but said conduit is always kept at an even temperature, most often above the freezing point also at low temperatures. Further, the conduit and the air drier are blown clean from water that can freeze to ice.
The object of the invention is to combine the advantages of the two well-known control modes described above. This is according to the invention attained in that in a separate signal air pipe from the air drier to the compressor there is a switch-over valve, operable between a first position, in which air passes through the valve for accomplishing a governor mode for the arrangement, and a second position, in which the air pipe from the air drier is closed and the air pipe to the compressor is open to the atmosphere for accomplishing an unloader mode for the arrangement.
In a preferred embodiment the valve is a 3/2 way valve, which is spring biased to the first position and automatically may be brought to the second position by means of an electrically energized solenoid controlled by a thermostat device.